1. Field of the Invention
The present invention relates to data communications, and more specifically to a receiver which can efficiently recover the data encoded in a high speed serial communication channel. The invention has particular application in digital display units such as flat-panel monitors.
2. Related Art
Receivers are often used to recover data received on a serial communication channel. In a typical scenario, an encoder encodes information (data) in the form of a sequence of symbols and a modulator generates a signal encoding the sequence of symbols in a serial communication channel. The receiver receives the signal and recovers the encoded symbols. Once the symbols are recovered, the information represented by the symbols may then be easily generated.
To recover the symbols encoded in a received signal, receivers often oversample the received signal to generate multiple samples per each symbol. Oversampling generally refers to sampling a signal more number of times than the number of symbols encoded in the signal. Typical receivers include a phase picker to select from among the samples, with the selected samples representing the symbols encoded in the received signal. Assuming for illustration that an input signal is oversampled by a factor of L (L being a positive integer), phase pickers are generally designed to select one out of L samples.
A prior receiver may determine an optimal sampling phase for a group of successive symbols, and select samples according to the optimal sampling phase. For example, an average sampling phase may be determined and be used as the optimal sampling phase. Such an approach is generally simple to implement, and may therefore be suitable in many situations.
However, such approaches may not be suitable in some environments. For example, due to conditions such as noise and channel mis-equalization, the symbol boundaries may get shifted. If the selection of samples is based solely on an optimal sampling phase (for a group of successive symbols), the selected samples may not accurately represent the encoded symbols due to the shifts.
The probability of such inaccuracies generally increases as the ratio of frequency of encoding to the bandwidth of the transmission medium is higher. Thus, in many media having limited bandwidth, when the symbols are encoded at high frequency, short shifts in the boundaries may lead to a symbol being skipped or more than one sample of a symbol being selected. In other words, if the boundaries shift to make the corresponding symbol period (the duration in which a symbol is encoded) short, the samples from a corresponding symbol may be skipped altogether. On the other hand if the symbol period is long, more than one sample may be selected for a corresponding symbol. Both the cases may be unacceptable at least in some situations.
One prior approach may increase the oversampling factor and examine the samples to determine the optimal samples representing the encoded data. However, receivers based on such high oversampling factor may require additional electrical power and also may result in increased overall cost to design and manufacture. At least in markets targeted for consumer markets, the increased costs and power requirements may not be acceptable.
Therefore, what is needed is a method and apparatus which enables a receiver to accurately recover data encoded in a serial communication channel at least while minimizing the cost and power requirements.